1. Field of the Invention
This invention relates to a control apparatus for a fuel pump, and particularly to a control apparatus having a function to control a pump for supplying fuel to an engine of a vehicle.
2. Description of the Related Arts
As shown in FIG. 10 for example, there is known a control apparatus 100 for a fuel pump 101 which has a power switching function for controlling fuel flow to an engine of a vehicle by changing the terminal voltage of the fuel pump 101 under a controller 103 which includes an FET (field effect transistor) 102 connected to the ground side of the fuel pump 101, and a pump stop function for surely stopping fuel supply to the engine by turning off a relay 105 which is connected in series with a power supply line 104 of the fuel pump 101 upon engine stopping.
Both the controller 103 and the relay 105 are controlled by a control signal transmitted from a computer 106 on the basis of the information of the vehicle's driving condition such as a throttle opening signal or vehicle speed signal, or only the relay 105 is controlled by a control signal transmitted from an air flow meter (not shown) on the basis of air intake to the engine. In FIG. 10, there are also shown a battery 109, a main relay switch 110, an input discriminating circuit 111 and a driver 112 for the FET 102.
In addition, JP-A-1-255497 discloses another control apparatus for a fuel pump, which is an improvement of the control apparatus 100 by removing the relay 105 of noisy working sound from the controller 103 by which the fuel pump 101 is stopped upon engine stop, in order to reduce the size of the apparatus, simplify the signal output lines 107, 108 and quiet the apparatus.
In this prior art, however, when a connection wiring conductor 113 which connects the fuel pump 101 and the FET 102 is made in contact with the body or bitten thereinto, the wiring conductor 113 is grounded because the vehicle's body is generally grounded. Also, when the signal output line 107 is similarly made in contact with the body or bitten thereinto, the signal output line 107 is grounded.
The result of the above cases is that the computer 106, upon engine stop, cannot stop the fuel pump 101 even by transmitting the control signal for stopping the fuel pump 101.
JP-A-60214 discloses an apparatus for protecting a semiconductor device, in which the operating condition is detected through voltage of the FET element detected by a current mirror MOS (metal oxide semiconductor) FET and the temperature of a power FET element is detected by detecting the forward voltage of the diode thermally connected to the power FET. This apparatus, however, merely detects the abnormal condition of the semiconductor device and protects the semiconductor device.
Therefore, the semiconductor device cannot be controlled so that the abnormal condition can be removed in accordance with the characteristic of the load which is controlled by the semiconductor device.